1. Field of the Invention
The present invention relates to a washing machine for washing laundry such as clothes, and more particularly, to a suspension apparatus of a washing machine which makes a washing tub suspended in a casing of the washing machine so as to minimize vibrations and noises generated when the washing machine is operated.
2. Description of the Related Art
In general, automatic washing machines for washing clothes by using agitated water currents may be classified into various types of washing machines depending on the driving system thereof or the type of a pulsator.
FIG. 1 is a vertical sectional view illustrating the internal structure of a conventional directly coupled motor type washing machine, and FIG. 2 is a vertical sectional view illustrating the internal structure of a conventional clutch type washing machine employing a pulsator.
First, the directly coupled motor type washing machine as shown in FIG. 1 is rotationally driven according to the operation of a motor 15 since an inner drum 12 is directly connected to the driving shaft 14 of the motor 15, a washing tub comprised of the inner drum 12 and an outer drum 13 is suspended by four suspension rods 16 in a casing 11 of the washing machine, and the motor 15 is positioned below the outer drum 13.
The driving shaft 14 of the motor 15 is connected to the inner drum 12 through the outer drum 13, and while the inner drum 12 rotates according to the operation of the motor 15, washing operation is performed.
On the other hand, in the clutch type washing machine, a pulsator 29 attached to the bottom surface of an inner drum 22 is rotated by a driving shaft 24 connected to a motor 25, and a clutch 28 is provided at the driving shaft 24 so that rotational power transmission can be connected or disconnected.
That is, the motor 25 is provided below an outer drum 23 of a washing tub, the motor 25 is connected to the driving shaft 24 via a pulley and a belt 27, and the clutch 28 is installed in the middle of the driving shaft 24 so that the rotational power transmission can be connected or disconnected.
In addition, while in the directly coupled motor type washing machine the motor directly drives the inner drum, the driving shaft 24 is connected to the pulsator 29 provided in the inner drum 22 as a rotating body, and washing operation is performed as the pulsator 29 is driven to rotate in a state in which the inner drum 22 does not rotate.
The outer drum 23 is connected to a casing 21 of the washing machine by four suspension rods 26 in a suspended manner as in the directly coupled motor type washing machine.
As described above, in both the directly coupled motor type washing machine and the clutch type washing machine, the inner and outer drums in which wash operation is performed are connected in the casing of the washing by the suspension rods as shown in FIG. 3. Referring to FIGS. 1 and 3, a suspension member 16a is installed at the upper end of the suspension rod 16 or 26 and fitted to a bracket 11a of the casing of the washing machine, and a damping force changing means 17 is installed at the lower end of the suspension rod 16 or 26 and performs damping function during the operation of the washing machine while supporting a bracket 13a of the outer drum.
In particular, the damping force changing means 17 is provided with a damper base 17a of a flange shape at the lower end of the suspension rod 16 as shown in FIG. 3, a damper spring 17b is disposed on the upper side of the damper base 17a, and a damper cap 17c which supports the outer drum 13 is capped over the damper spring 17b. 
Therefore, the load generated from the inner and outer drums is transferred to the damper spring 17b via the damper cap 17c, and at this time the damper spring 17b does buffering function while being supported by the suspension rod 16.
Since, the distribution of laundry is not symmetrical with respect to the rotating shaft at the early stage of an extraction phase, eccentric load occurs in the washing tub, and accordingly vibrations and noises may be severely generated.
To form a damping force for buffering such vibrations is an important role of the damping force changing means 17. That is, the damping force converts kinetic energy into thermal energy, etc. to decrease the amplitude of the vibrations, and is, in the damping force changing means 17, generated by a friction force ++++between the damper base 17a and the damper cap 17c and the flow of air into or out of the damping force changing means 17.
However, there is a problem in which when the conventional suspension apparatus employing the suspension rods 16 as described above is designed to have a greater damping force so as to suppress abnormal vibrations due to eccentric load generated at the early stage of an extraction phase, the amplitudes of noises become larger during the normal operation of the washing machine, and when the suspension apparatus is designed to have a lesser damping force so as to decrease the amplitudes of noises generated during the normal operation, excessive vibrations are generated at the early stage of the extraction phase and accordingly walking phenomena of the washing machine may occur.
Consequently, unless a damping force which satisfies the characteristics required during the early stage of the extraction phase and during the normal washing operation is formed, most portions of the vibrational forces generated at the inner and outer drums 12 and 13 are transferred to the casing 11 of the washing machine via the suspension rods 16, the amplitude of the vibrations of the casing 11 is more increased by the components of the transferred vibrational forces which are near to the resonant frequency of the casing 11. Therefore, the suspension rods 16 and the outer drum 13 are also vibrated, and accordingly more noises are generated when the washing machine is operated.
To solve the above problems, it is an objective of the present invention to provide a suspension apparatus of a washing machine which is capable of minimizing vibrations and noises by changing the structure of a damping force changing means so that the damping force of the damping force changing means can vary with acting load generated when the washing machine is operated.
To achieve the above objective, there is provided a suspension apparatus of a washing machine comprising:
suspension rods the upper portions of which are connected to a casing of the washing machine and the lower portions of which are connected to a washing tub so that the washing tub can be supported in the casing in a suspended state;
damper bases installed at the respective lower ends of the suspension rods;
damping force changing means fitted around the respective suspension rods and positioned above the respective damper bases, so as to be compressed according to the variations in load of the washing tub and change the damping force generated when contacting the respective suspension rods; and
elastic means installed between the damping force changing means and the damper bases, respectively, so as to do buffering action, and, in addition, providing compression forces for the damping force changing means, respectively.